There are a large number of known and conventional screw caps and methods of closing container mouths, in particular the mouths of bottles. In such arrangements, the screw cap is generally fitted on to the mouth of the container and then screwed on by means of a screwing-on head, with a predeterminable screwing torque. Screw closures of this kind are described for example in commonly assigned German patent applications Nos. P 25 29 289 and P 28 11 741. Screwing-on heads for closing containers by means of screw caps of that kind are disclosed for example in commonly assigned German patent application No. P 28 52 150.8.
In practice, screw caps of this kind have been extremely successful. In particular, they are superior for some uses to snap-on closures such as are disclosed in H. W. Williams' U.S. Pat. No. 3,223,269. Such snap-on closures have a screw-thread with a pitch which differs from the pitch of the screw-thread on the bottle. This means on the one hand, that, it is not possible to arrive at a surface contact between the threads but only a punctiform contact, and on the other hand, that the cap will probably be tilted on the neck of the container. In addition, with such an arrangement, the depth by which the internal seal penetrates into the neck of the bottle is random so that the internal surface of the neck of the bottle must be formed as a sealing portion over a relatively wide area. This makes it impossible to use so-called head seals which are arranged on the end plate portion of the cap and which co-operate with the rim of the mouth of the container. Seals of this kind, at least as an additional seal, are advantageous in particular for use in relation to CO.sub.2 -bearing drinks.